soc/intel/common: Bring DISPLAY_MTRRS into the light

Initially, I wanted to move only the Kconfig DISPLAY_MTRRS into the
"Debug" menu. It turned out, though, that the code looks rather generic.
No need to hide it in soc/intel/.

To not bloat src/Kconfig up any further, start a new `Kconfig.debug`
hierarchy just for debug options.

If somebody wants to review the code if it's 100% generic, we could
even get rid of HAVE_DISPLAY_MTRRS.

Change-Id: Ibd0a64121bd6e4ab5d7fd835f3ac25d3f5011f24
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/29684
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/quark/include/soc/ramstage.h

@@ -17,6 +17,7 @@
 #ifndef _SOC_RAMSTAGE_H_
 #define _SOC_RAMSTAGE_H_
 
+#include <arch/cpu.h>
 #include <chip.h>
 #include <device/device.h>
 #if IS_ENABLED(CONFIG_PLATFORM_USES_FSP1_1)